Electroslag ingot production

ABSTRACT

The electroslag process of ingot production in a mold is improved by providing bottom contact to the forming ingot by means of a stub or spigot which is electrically insulated from the mold base and also has electrical connection made to it in a manner electrically insulated from the mold base.

United States Patent Inventor Adrian Paul Simmons Lichtield, EnglandAppl. No. 701,723 Filed Jan. 30, 1968 Patented Oct. 5, 1971 AssigneeAssociated Electrical Industries Limited London, England Priority Aug.23, 1967 Great Britain 38887/67 ELECTROSLAG INGOT PRODUCTION [56]References Cited UNITED STATES PATENTS 587,138 7/1897 Roberts 13/232,711,955 6/1955 Jordan 164/52 X 3 ,3 89,208 6/1968 Roberts et 211..13/9 3,129,473 4/1964 Veil, Jr. 164/252 469,454 2/1892 Rogers 13/23 X2,375,107 5/1945 Hopkins M 75/10 Primary Examiner-J Spencer OverholserAssistant Examiner-V. K. Rising Attorney-Bowyer & Witherspoon ABSTRACT:The electroslag process of ingot production in a base.

PATENTEU GET 5 I97! 1 ELECTROSLAG INGOT PRODUCTION CROSS-REFERENCE TOPRIOR PATENT BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to the so-called electroslag process of producingingots of metal, which word is used herein as .connoting not onlyelemental metals but also, in accordance with an important present dayuse of this process, metal alloys such for instance as various types ofsteel.

2. Description of Prior Art In such an electroslag process, an electrodeof metal from which an ingot is to be produced, orpossibly of unalloyedconstituents of an alloy to be produced as an ingot, is supported withits lower end depending into an ingot mold and there immersed in ablanket of molten slag over a pool of molten metal. The lower end of theelectrode is spaced from the surface of this molten pool and isprogressively fused off to enter the pool by heat which is generated bythe passage of electric current through the slag. The slag not onlyshields the metal pool from contaminating gases but can also be sochosen that it acts to' segregate and absorb impurities from the moltenmetal in its passage through the slag from the electrode to the moltenpool. The mold wall, and usually also the mold base, are continuouslycooled, so that, as the'process proceeds, the molten metal solidifiesprogressively upwardly from the bottom and thereby forms a progressivelylengthening ingot which is separated from the moldat the end of theprocess.

In single-phase operation of the 'electroslag process, (including thesimultaneous formationof a number of ingots in individual molds withindividual electrodes energized in parallel from a single-phase-line)and in multiphase, e.g., threephase, operation with individual molds (asdistinct from multiphase modes of operation in which, with at leastthree electrodes in a single mold, the operation proceeds by virtueofelectrode-ingot-electrode current flow without requiring electricalcontact to the bottom of the ingot) the operation is dependent oncontinuity of current flow through the slag and the ingot metal betweenthe electrode in the (or each) mold and a bottom contact to the ingot.Where, as is common, the mold base is used for providing the bottomcontact to the ingot, trouble is sometimes experienced due to loss ofelectrical conduction between the bottom of th'eingot and the mold base.Such loss of conduction is liable to occur if any sticking occursbetween the bottom of the ingot and the mold base. Such loss ofconduction is liable to occur if any sticking occurs between the ingotand the mold walls, because shrinkage of the cooling ingot between themold base and the sticking location tends to cause the bottom of theingot to lift off the base. As it is undesirable for electric current toflow in the mold walls, it is common practice to insulate the mold wallsfrom the base in order to prevent such current flow. Thereforetheshrinkage effect just. described can result in the interruption ofthe process current and consequent stopping of the process. Moreover,immediately before such interruption of the current a hot spot or localarcing'may develop at the last point of contact with the mold base andthis may seriously damage the mold base.

Loss of conduction may also occur due to the formation,

between the ingot bottom and the mold base, of a thin layer or skin ofsolidified slag the conductivity of which, over the whole or part of itsarea, has become so attenuated by cooling as to impair the operation ofthe process. Provided the slag which forms such a layer remainssufficiently hot, its conductivity is sufficiently high for the processto continue. However, as the ingot solidifies upwardly as the processprogresses, there is a tendency for the slag layer to become cooler andto lose its high conductivity except where it is locally heated bycurrent passing through a restricted region or regions of its totalarea. Such region or regions may contract'in size and/or reduce innumber as the process continues, until either the current is interruptedor the localized heating produced by a high current flowing through aremaining region of relatively small area is sufficient to damage themold base.

In the case of a'multiphase operation in a single mold, the

formationof the ingot can be concluded by a hot-topping" procedureperformed by withdrawing all but one of the electrodes and continuingthe process in single-phase mode with the remaining electrodecentralized in the. mold, e.g. by appropriate sideways displacement ofthe latter on a wheeled support. ln such a case, loss of bottom contactto the ingot during the multiphase operation could prevent thesubsequent single-phase hot-topping step from proceeding. Moreover, lossof contact is more likely to occur with such multiphase operation thanwith single-phase operation, because in the latter the flow of currentbetween the ingot bottom and the mold base'has some tendency to keep-athin slag film between the ingot and mold base in an electricallyconductive state.

SUMMARY OF THE INVENTION I According to the present inventionmaintenance of current connection to the bottom of the forming ingot isensured by the provision at the bottom of the ingot of a stub or spigotwhich, extending through an opening in the mold base and being ofmaterial not incompatible with that of the ingot is electricallyinsulated from the mold base and has electrical connection made to it ina manner also electrically insulated from the mold basefto providebottom connection to the ingot, the cross section of the stub or'spigotbeing smaller than the ingot cross section but being sufficiently greatto carry the process current without fusing, taking into account anycooling effective on the stub or spigot.

In this way, bottom connection to the fonning ingot is maintaineddirectly via the connecting means andstub, so that lifting of the ingotbottom from the mold base due to shrinkage is no longer a problem. Also,because no current needs to pass through the mold base or between it andthe bottom of the ingot, it is possible to make the mold base of arelatively cheap material, e.g., mild steel, which does not need to besuitable for carrying current. Additionally the elimination of currentflow between the ingot and mold base reduces surface erosion.

By a material not'incompatible with that of theingot is meant one whosecomposition is the same as the ingot composition or at least iscompatible with it.

BRIEF DESCRIPTION OF THE DRAWING The single FIGURE of theaccompanyingdrawing is a somewhat schematic. sectional elevation of anelectroslag process mold showing the provision of'an ingot bottomcontact stub in accordance with the invention.

DESCRIPTION OF PREFERRED EMBODIMENT In the drawing, l'represents themold wall, (commonly but not necessarily cylindrical) insulated from themold base 2 by insulating and sealing material 3; Awater sprayarrangement 4 round the topof the mold wall 1 produces a curtain 5 ofcooling water which flows down the wall and is collected in a drainagetrough 6 round the bottom of the wall. This trough 6 can with advantagebe constructed as described in Maskall application Ser. No'..629, 746now U.S.-Pat. No. 3,448,790. The mold base 2 has a cooling jacket 7. Forforming an ingot 8 by the electroslag process an electrode 9 (or anumber of such electrodes) depends-into the mold with the lower enddipping into a layer of molten slag 10. Electric current is passedthrough the slag'and the forming ingot between the electrode 9 and abottom connection to the ingot. (The manner in which this bottomconnection is ensured in the illustrated arrangement will be describedlater.) The passage of the current through the slag 10 keeps it initsmolten state and causes the electrode 9 to be progressively melted offat its lower end. The moltenelectrode material falls through the slaginto a molten pool 11 at the top of the forming ingot. As the processproceeds the ingot progressively solidifies upwards from the bottom, dueto the cooling of the mold. At the end of the process, the solidifiedingot is separated from the mold.

In accordance with the invention, a preformed stub 18 (which becomeswelded to the bottom of the ingot at the beginning of the process)projects through an opening for it in the mold base and is insulatedfrom the mold base and its cooling jacket by an annulus 19 ofheat-resisting, electrically insulating material such as alumina,accommodated round the stub within the stub opening in the mold base.The annulus 19 may be a preformed member or may be formed in situ (withthe lower end of its accommodating space initially closed) bysolidification of slag poured into the mold in molten state at thebeginning of the ingot-forming process.

The stub 18 is gripped by a connecting clamp 20 which is supportedbeneath the mold base and is insulated from the latter. For this purposethe clamp 20 is indicated as being supported by brackets 21 withintervening electrical insulation 22. Supply return conductors 23 areconnected to the clamp 20, which in this case is preferably providedwith its own cooling circuit, as indicated at 24, because theintervening insulation 22 tends to isolate it from the cooling systemfor the mold base. The provision of insulation (3) between the mold wall1 and mold base 2 could possibly be dispensed with because the mold baseitself is now electrically isolated, but water sealing would, however,still be desirable.

When the ingot is ready for removal from the mold the clamp can bereleased and the stub can be withdrawn through the clamp by (upward)withdrawal of the ingot. The stub may then be cut off the bottom of theingot and reused.

I claim: 1. An electroslag mold apparatus comprising, in combination:

a. a mold base, b. a mold wall upstanding from said mold base andforming a mold cavity,

c. an opening in said mold base, said opening having a cross sectionsmaller than the internal cross section of said mold cavity,

d. an annulus positioned in said opening, said annulus being fonned ofelectrically insulative material,

e. an electroconductive stub positioned within said annulus andelectrically insulated from said mold base by said annulus,

f. means for establishing electrical connection to said stub,

and

g. clamp means supported by said base.

2. The apparatus of claim 1 and including electrically insulatingmaterial between said clamp and said base.

3. The apparatus of claim I and including water-cooling means for saidclamp.

4. The apparatus of claim I and including electrically conductive meansmounted on said clamp.

S. The apparatus of claim I wherein said stub and said clamp areelectrically connected.

6. The apparatus of claim 5 wherein said stub is formed in situ withinsaid annulus.

1. An electroslag mold apparatus comprising, in combination: a. a moldbase, b. a mold wall upstanding from said mold base and forming a moldcavity, c. an opening in said mold base, said opening having a crosssection smaller than the internal cross section of said mold cavity, d.an annulus positioned in said opening, said annulus being formed ofelectrically insulative material, e. an electroconductive stubpositioned within said annulus and electrically insulated from said moldbase by said annulus, f. means for establishing electrical connection tosaid stub, and g. clamp means supported by said base.
 2. The apparatusof claim 1 and including electrically insulating material between saidclamp and said base.
 3. The apparatus of claim 1 and includingwater-cooling means for said clamp.
 4. The apparatus of claim 1 andincluding electrically conductive means mounted on said clamp.
 5. Theapparatus of claim 1 wherein said stub and said clamp are electricallyconnected.
 6. The apparatus of cLaim 5 wherein said stub is formed insitu within said annulus.